This application is based upon and claims priority of Japanese Patent Application Nos. 2000-255646 and 2001-202730, filed on Aug. 25, 2000 and Jul. 3, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to semiconductor devices, manufacturing methods of the same, and semiconductor manufacturing apparatus, in particular, for being suitably applied to a so-called system-on panel, in which a pixel region including thin film transistors and a peripheral circuit region including thin film transistors are formed on a non-crystallized (amorphous) substrate such as a non-alkali glass substrate.
2. Description of the Related Art
A TFT (Thin Film Transistor) is formed on a very thin, fine active semiconductor film. The TFT is examined to be mounted on a large-screen liquid crystal panel or the like in consideration of recent demands for an increase in area. In particular, applications to a system-on panel and the like are expected.
On the system-on panel, polycrystalline semiconductor TFTs (especially polysilicon TFTs (p-Si TFTs)) are formed on a non-crystallized substrate such as a non-alkali glass substrate. In this case, as a popular method, an amorphous silicon (a-Si) film is formed as a semiconductor film, and then irradiated with an ultraviolet short-pulse excimer laser to fuse and crystallize only the a-Si film without influencing the glass substrate, thereby obtaining a p-Si film functioning as an active semiconductor film.
Excimer lasers which emit high-output linear beams coping with a large area of the system-on panel have been developed. A p-Si film obtained by excimer laser crystallization is readily influenced by not only the irradiation energy density but also the beam profile, the state of the film surface, or the like. It is difficult to form uniformly a p-Si film large in crystal grain size in a large area. A sample crystallized by an excimer laser was observed with an AFM to find that crystal grains isotropically growing from nuclei produced at random exhibited a shape close to a regular polygonal shape, projections were observed at a crystal grain boundary at which crystal grains collided against each other, and the crystal grain size was less than 1 xcexcm, as shown in FIG. 37.
In this manner, when a TFT is fabricated using a p-Si film obtained by crystallization using an excimer laser, a channel region contains many crystal grains. If the crystal grain size is large, and the number of grain boundaries present in the channel is small, the mobility is high. If the crystal grain size at a channel region portion is small, and the number of grain boundaries present in the channel is large, the mobility is low. Thus, the transistor characteristics of the TFT readily vary dependently on the grain size. In addition, the crystal grain boundaries have many defects, and the presence of the grain boundaries in the channel suppresses transistor characteristics. The mobility of the TFT attained by All this technique is about 150 cm2/Vs.
It is an object of the present invention to provide semiconductor devices including TFTs in which the transistor characteristics of the TFTs are made uniform at a high level, and the mobility is high particularly in a peripheral circuit region to enable high-speed driving in applications to peripheral circuit-integrated TFT-LCDs, system-on panels, system-on glasses, and the like.
It is another object of the present invention to provide semiconductor devices in which the insufficiency of the output of an energy beam, which outputs energy continuously in relation to time, is compensated so that the throughput in crystallization of semiconductor films is improved, thereby realizing highly efficient TFTs whose mobility is high particularly in a peripheral circuit region to enable high-speed driving.
It is still another object of the present invention to provide manufacturing methods of such semiconductor devices.
It is still another object of the present invention to provide apparatus for manufacturing such semiconductor devices.
According to the first aspect of the present invention, there is provided a method of manufacturing a semiconductor device in which a pixel region having thin film transistors and a peripheral circuit region are formed on a non-crystallized substrate, comprising crystallizing a semiconductor film formed in the peripheral circuit region with an energy beam which outputs energy continuously along a time axis at least for the peripheral circuit region, thereby forming the semiconductor film into active semiconductor films of the respective thin film transistors.
In this case, the energy beam is preferably a CW laser beam, more preferably, a solid state laser beam (DPSS (Diode Pumped Solid State Laser) laser beam).
By crystallizing a semiconductor film with an energy beam which outputs energy continuously along the time axis, the crystal grain size is increased, e.g., the crystalline state of the semiconductor film is formed into a streamlined flow pattern having long crystal grains in the energy beam scan direction. The crystal grain size in this case is 10 to 100 times the size obtained by crystallization using a currently available excimer laser.
In the first aspect, each semiconductor film is preferably patterned into a linear or island shape on the non-crystallized substrate.
The crystallization technique using a CW laser has conventionally been studied in the SOI field, but a glass substrate has been considered not to resist heat. When a glass substrate is irradiated with a laser while an a-Si film is formed as a semiconductor film on the entire surface, the temperature of the glass substrate rises along with the temperature rise of the a-Si film, and damage such as cracks is observed. In the present invention, the semiconductor film is processed into a linear or island shape in advance to prevent the temperature rise of the glass substrate, generation of cracks, and diffusion of impurities into a film. Even in forming the active semiconductor film of a TFT on a non-crystallized substrate such as a glass substrate, an energy beam which outputs energy continuously along the time axis from a CW laser or the like can be used without any problem.
In the first aspect, an energy beam irradiation positioning marker corresponding to each patterned semiconductor film is formed on the non-crystallized substrate.
This marker can suppress an irradiation position shift of the energy beam. Supply of a stable continuous beam enables so-called lateral growth, and a semiconductor film having large-size crystal grains can be reliably formed.
In the first aspect, it is preferable that slits be formed in each semiconductor film patterned on the non-crystallized substrate, or thin-line insulating films be formed on each semiconductor film, and the semiconductor film be irradiated with the energy beam in an almost longitudinal direction of the slits.
In this case, the slits or insulating films (to be simply referred to as slits hereinafter for convenience) block crystal grains and grain boundaries which grow inward from the periphery in crystallization by irradiation of an energy beam. Only crystal grains which grow parallel to the slits are formed between the slits. If the region between the slits is satisfactorily narrow, single crystals are formed in this region. In this manner, the channel region can be selectively changed into a monocrystalline state by forming the slits so as to set a region where large-size crystal grains are to be formed, e.g., the region between the slits as the channel region of a semiconductor element, e.g., thin film transistor.
In the first aspect, it is preferable that an irradiation condition of the energy beam which outputs energy continuously along the time axis be changed between the pixel region and the peripheral circuit region, that a semiconductor film formed in the pixel region be crystallized with an energy beam which outputs energy pulses, and the semiconductor film formed in the peripheral circuit region be crystallized with the energy beam which outputs energy continuously along the time axis (more specifically, the semiconductor film formed in the pixel region be crystallized, and then the semiconductor film formed in the peripheral circuit region be crystallized), or that the semiconductor film formed in the peripheral circuit region be crystallized with the energy beam which outputs energy continuously along the time axis, the crystallized semiconductor film be set as an active semiconductor film, and a semiconductor film formed in the pixel region be set as an active semiconductor film without any change.
Although positional controllability is important for either of the pixel and peripheral regions, any thin film transistor formed in the peripheral circuit region requires higher performance than that in the pixel region, and must be optimized in fabrication. For this purpose, an energy beam which continuously outputs energy and can reliably form an active semiconductor film having large-size crystal grains and make the operation characteristics of respective thin film transistors uniform at high level is applied particularly to the peripheral circuit region. In the pixel region where the required performance is low, the energy beam irradiation time is shortened, or a pulse-like energy beam is applied. In this way, the crystallization process is changed between the peripheral circuit region and the pixel region. Accordingly, a desired system-on panel which very efficiently satisfies the required performance of respective locations can be implemented.
According to the second aspect of the present invention, there is provided a semiconductor device in which a pixel region having thin film transistors and a peripheral circuit region are formed on a non-crystallized substrate, wherein active semiconductor films of the respective thin film transistors constituting at least the peripheral circuit region are formed into a crystalline state of a streamlined flow pattern having large crystal grains.
In this case, the active semiconductor film can be changed into a large-crystal-grain state, and preferably a monocrystalline state along the streamlined shape of the flow pattern. For example, the channel region of a thin film transistor can be changed into a monocrystalline state. A high-speed-driving thin film transistor excellent in transistor characteristics can be implemented.
Besides, the semiconductor film is preferably formed over the non-crystallized substrate with a buffer layer being interposed between them. The buffer layer includes a thin film containing Si and N, or Si, O, and N. The density of hydrogen in the semiconductor film is preferably 1xc3x971020/cm3 or less, more preferably, the density of hydrogen in the buffer layer is 1xc3x971022/cm3 or less.
By this construction, the transistor characteristics of the TFTs can be uniformized at a high level using crystallization with an energy beam that outputs energy continuously in relation to time. Further, the TFTs can stably be formed without generation of pinholes or peeling-off. Very highly reliable TFTs can be realized thereby.
According to the third aspect of the present invention, there is provided a semiconductor manufacturing apparatus for emitting an energy beam for crystallizing a semiconductor film formed on a non-crystallized substrate, wherein the semiconductor manufacturing apparatus can output the energy beam continuously along a time axis, and has a function of scanning the energy beam to an object to be irradiated, and output instability of the energy beam has a value smaller than xc2x11%.
In this case, the output instability of the energy beam is set to a value smaller than xc2x11%, and more preferably noise representing the instability of the energy beam with respect to the time is set to 0.1 rms % or less. A stable continuous beam can therefore be supplied. The continuous beam can be scanned to form uniformly the active semiconductor films of many thin film transistors in a large-size crystalline state (flow pattern).
According to the fourth aspect of the present invention, like the third aspect, there is provided a semiconductor manufacturing apparatus. The apparatus comprising disposing means for disposing a non-crystallized substrate on a surface of which a semiconductor film is formed, so that the non-crystallized substrate can freely be moved in a plane parallel with a surface of the semiconductor film, laser oscillation means that can output an energy beam continuous in relation to time, and beam splitting means for optically splitting the energy beam emitted from the laser oscillation means, into sub-beams. Each of the sub-beams is applied to relatively scan the corresponding portion of the semiconductor film to crystallize.
In this case, with the split sub-beams, the predetermined portions of the semiconductor film corresponding to the respective sub-beams can be crystallized at once. Thus, each of the active semiconductor films of many thin film transistors can be formed uniformly in a large-size crystalline state (flow pattern). Besides, even when using laser oscillation means whose output is lower than those of excimer lasers, such as a CW laser, a very high throughput not inferior to those in case of using excimer lasers can be obtained. Crystallization for thin film transistors can efficiently be achieved thereby.
In the fourth aspect, each sub-beam is preferably controlled so that only the portion where a thin film transistor is to be formed is irradiated with the beam at the optimum energy intensity for crystallization and the beam rapidly pass the portion where no thin film transistor is to be formed. A higher throughput can be obtained thereby, and very highly efficient crystallization for thin film transistors can be realized.
According to the fifth aspect of the present invention, like the third aspect, there is provided a semiconductor manufacturing apparatus. The apparatus comprising disposing means for disposing a non-crystallized substrate on a surface of which a semiconductor film is formed, so that the non-crystallized substrate can freely be moved in a plane parallel with a surface of the semiconductor film, laser oscillation means that can output an energy beam continuous in relation to time, and intermittent (pulse) emission means having a transmission area and an interruption area for the energy beam to intermittently transmit the energy beam. With moving the energy beam to relatively scan the non-crystallized substrate, the energy beam is intermittently applied to the semiconductor film to selectively crystallize only the portion where a thin film transistor is to be formed.
In this case, by controlling the transmission of the energy beam mainly with the intermittent emission means, only desired portions of the semiconductor film can be selectively crystallized. That is, only desired portions of the semiconductor film in the non-patterned state can be selectively crystallized. Therefore, it is needless to set up in advance the portions to be irradiated with the beam, i.e., the portions (ribbon-like or island-like) where thin film transistors are to be formed. As a result, the number of manufacturing steps can be reduced and the throughput can be improved.
In the fifth aspect, it is preferable that the energy beam is intermittently applied to certain portions other than where thin film transistors are to be formed, so as to form positioning markers for the thin film transistors each crystallized into a predetermined shape. By forming the positioning markers simultaneously with the crystallization of where thin film transistors are to be formed, the number of manufacturing steps can be reduced and efficient and accurate formation of the thin film transistors becomes possible.
The present invention includes semiconductor devices and manufacturing methods of the semiconductor devices, corresponding to the above fourth and fifth aspects.